code: def __len__(self) -> int:
      return 10
  
file_path: lightning-flash/tests/core/test_data.py
imports: import pytest
  import torch
  from flash import DataKeys, DataModule, RunningStage
  from flash.core.data.data_module import DatasetInput
  from flash.core.utilities.imports import _TOPIC_CORE_AVAILABLE
label_desc: Use image node_id 2 for calling the DummyDataset obj's underlying member method code with example usage: obj.__len__() and returns: int